Apparatus for and method of controlling the firing of seismic sound sources

ABSTRACT

A digital control system for establishing preset delays in firing a plurality of pneumatic sound sources. Predetermined firing command delays between system triggering and source triggering are set by appropriately setting each of a plurality of digital switches associated with the sources. As the elapsed time represented by a count in a command delay register and each of the predetermined delay times set by the switches becomes equal as determined by a coincidence detector, fire commands are generated for each of the sources. After the sources are fired, counts accumulated in firing delay registers associated with the sources are terminated and the counts, which correspond to the delays between triggering and actual firing of the sources, are displayed.

United States Patent Ritter Sept. 29, 1972 APPARATUS FOR AND METHOD OFCONTROLLING THE FIRING OF Primary Examiner-Benjamin A. BorcheltAssistant Examiner-H. A. Birrniel SEISMIC SOUND SOURCES Attorney-WilliamJ. Scherback, Frederick E. Dumou- [72] Inventor Sammie}? Rm D atlas Texlin, Arthur F. Zobal, Andrew L. Gaboriault and Sidney A. Johnson [73]Assignee: Mobil Oil Corporation 221 Filed: Sept. 28, 1970 [57] ABSTRACT[21] APPL No: 76,126 digital control system for establishing presetdelays in finng a plurality of pneumatic sound sources. Predeterminedfiring command delays between system U-S. FS, H, R, and ource are setappropriate- 324/188 340/7R 1y setting each of a plurality of digitalswitches as- [gilg] gilt-l ..G0lv l/08 sociated with the sources AS theelapsed time 1 e 0 Search "324/188, Isl/0'5 represented by a count in acommand delay register 181/0'5 H; 340/7 R; 317/80 and each of thepredetermined delay times set by the switches becomes equal asdetermined by a coin- [56] References cued cidence detector, firecommands are generated for UNITED STATES PATENTS each of the sourcesAfter the sources are fired, counts accumulated in firing delayregisters associated with g lli et a1 the sources are terminated and thecounts, which correspond to the delays between triggering and actual gzi zzz firing of the sources, are displayed.

6 Claims, 6 Drawing Figures l w l i swncmzs no i l l l I i B PC con.CURRENT swn'cHEs RHEOSTATS suns FIRING i F/cz V A A 1 COMMAND c v -v 2"wa +1 I 3 t 3 I |2 I A --"4 P60 1 CONTROL SYSTEM l l4 I RE lNG L I T2 Hme. tiiPt I DELAY l i T84, l l I i I P'IIIENTEIIIIIQZ Ian 31581.21 8

SHEEI 3 0F 6 {FCQ r- SWITCH lO-3 ,J y SWITCH I01 J FIRING J COMMAND LDELAY CONTINUOUS SWITCH lO-4 SETTINGS COUNT- SWITCH I0-2 ELAPSED ZEROCOUNT LEvEL SYSTEM TRIGGERING |AI/FC'I rT Fcg F FIRING Fl/ 63 COMMANDS(TB1 TBQUT TB i 2 s FIRING TB I'L/ 4 (D l LIJ LU .J

DISPLAYED j COUNT- FIRING DELAY FOR 2 GUN Nos.l,2,38I4 9 U)lllllllll'llllllllll 0 5 IO I5 20 Ms. (Milliseconds) Fig. 3

SHEET 5 OF 5 RESET TENIS REGISTER UNII'S REGISTER TO I6-1 TENS REGISTERUNITS REGISTER T i 2 2 m H W 6 m 8* 2 8 I/ 2 R TIE V w R VQ IIG E S NILVI E V TI E E 3 6 3 W V m v V m LV E T wI G E V R 5 w w VO IN I TOI6-3 TENS REGISTER UNITS REGISTER APPARATUS FOR AND METHOD OFCONTROLLING THE FIRING OF SEISMIC SOUND SOURCES FIELD OF THE INVENTIONThis invention relates to systems for controlling the firing of aplurality of seismic sound sources.

In marine seismic exploration, a plurality of seismic sound sources areoften utilized in order to shape a time and the predetermined firingcommand delay times of the respective sound sources. As coincidencesbetween the elapsed time and the predetermined firing command delays aredetected, firing commands are given to the respective sound sources.

In accordance with another aspect of this invention,

the delays between system triggering and actual firings of the soundsources are displayed thereby indicating any necessary adjustment in thesetting of the variable seismic energy wave front. In some instances,the firing command delay times in order to compensate for seismic soundsources or guns are positioned at different depths and the guns arefired at different times to achieve reinforcement of the primary pulseand cancellation of the bubble pulse. In other instances, the guns arepositioned at the same depth and fired simultaneously.

It is of course desirable to precisely control the firing times of theseismic sound sources in order to appropriately shape the seismicwavefront. Considerable difficulties arise in achieving this precisecontrol without sacrificing the flexibility of the system; i.e., theability to set different firing times for different circumstances.Additional difficulties arise when pneumatic sound sources are utilizedwhich have characteristic firing delays defined as the time lapsebetween source firing command and source firing. The characteristicfiring delay of any given pneumatic sound source can change aftercontinued use thereby increasing the difficulties in achieving precisecontrol.

DESCRIPTION OF THE PRIOR ART The prior art control systems for firing aplurality of seismic sound sources have not provided suflicientlyflexible nor precise control of the sound source firing times. Forexample, U.S. Pat. No. 3,304,533 Huckabay discloses a control systemcomprising a decade counter tube which establishes a fixed firingsequence for a plurality of sound sources in response to pulsesgenerated by an oscillator. As a result, it is not possible toindependently vary the firing times of the sound sources nor is itpossible to fire the sound sources simultaneously. Of course, it is notpossible to compensate for changes in the characteristic firing delaysof the sound sources. Such changes are a particular problem withpneumatic sound sources.

Furthermore, the prior art control systems for firing a plurality ofsound sources do not indicate the delay between triggering the controlsystem and actual firing of the sound sources. As a consequence, thereis no indication as to when the control system fired the sound sourcesnor is there any indication of the characteristic firing delays of thesound sources or changes in the characteristic firing delays.

SUMMARY OF THE INVENTION In accordance with one aspect of the invention,the firing times for a plurality of seismic sound sources are variablypreset. This aspect of the invention may be provided by a digitalcontrol system comprising means for triggering the system and means forvariably presetting a predetermined firing command delay time withrespect to system triggering for each of the sound sources. The systemfurther comprises means for determining the elapsed time after systemtriggering and means for detecting coincidences between the elapsedunknown or varying characteristic delay times of the.

sound sources.

This aspect of the invention may be provided by. a. digital controlsystem comprising means for determining the elapsed time between systemtriggering and firing of each sound source and further comprising meansfor displaying this elapsed time for each source.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a seismicexploration system utilizing a control system embodying the invention;

FIG. 2 is a block diagram of the control system of FIG. 1;

FIG. 3 is a timing diagram for the system of FIG. 2;

FIGS. 4a and 4b are matched schematic diagrams of some of the digitalcircuitry of FIG. 2; and

FIG. 5 is a schematic diagram of a portion of the coincidence detectorof FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 discloses a seismicexploration system utilizing a control system for firing or triggeringpneumatic sound sources or guns 1, 2, 3, and 4. The control system maybe programmed by switch means 10 including four switches correspondingto guns 1, 2, 3, and 4 so as to fire the guns simultaneously or in anystaggered relationship thus developing a directivity in the resultingseismic energy wavefront. A firing command FC, or trigger signal whichis generated by a recording system operating in a timed mode or arecording system operating in a composite mode is then applied to afiring command delay means 12 through a switch 13 to initiate the firingcycle. When the time elapsed after the system firing command FC equalsthe programmed firing command delays set with switches I0, firingcommands FC,, FC FC; and PC, are generated and applied to four coilcurrent switches and coil current controlling rheostats associated withguns 1, 2, 3, and 4.

The guns I, 2, 3, and 4 do not fire immediately upon receiving thefiring commands FC FC PC and FC since each gun has a characteristicfiring delay before the lid moves and exhausts the compressed air. Wheneach lid does move corresponding to actual firing, a time break TB isgenerated for each gun. The time breaks TB TB TB;, and TB, for the guns1, 2, 3, and 4 are then applied to a means 14 for determining the actualfiring delays which are then indicated at a display means 16 includingfour indicators. The earliest of the time breaks TB TBg, TB and TB, isapplied to the recording systems.

As shown in FIG. 2, the digital control system embodying the inventionis further detailed in block diagram fonn. The switch means 10 includesa plurality of thumbwheel digital switches -1, 10-2, 10-3, and 10-4calibrated in ms. (milliseconds) associated respectively with the fourpneumatic sound sources or guns 1, 2, 3, and 4 (not shown). The settingof any one switch presets a particular firing command delay time for therespective gun; i.e., a predetermined delay between the system firingcommand FC, and the respective gun firing commands FC FC PC and Thefiring command delay means 12 comprising a lKI-I source 18 of gatedclock pulses is coupled to units and tens decade counters 20 and 22 toproduce a continuously accumulating count throughout the firing cyclerepresenting the time elapsed since system triggering. A coincidencedetector 24 detects a coincidence between the firing command delaysestablished by the digital switches 10-1, 10-2, 10-3 and 10-4 and thecontinuously accumulating count in the decade counters 20 and 22 whichcorresponds to elapsed time in ms. The firing commands FC FC PC and FC.are then applied to the respective guns in response to the detectedcoincidences.

The actual firing delay means 14 also comprises decade counters whichaccumulate counts corresponding to the elapsed time between the systemfiring FC, and the time breaks TB,, TB TB and TB In order to determinethe actual firing delay for each gun, units and tens decade counters 26and 28 are associated with each gun. Upon receiving a time break TB, aflip-flop 30 associated with each gun is reset and the countaccumulating in the corresponding decade counters 26 and 28 isterminated. This count can then be displayed at an appropriate one ofthe display units 16-1, 16-2, 16-3, and 16-4. A time break TBcorresponding to the earliest of the time breaks T8,, TB T8 and TB, isobtained from NAND gate 32.

The operation of the digital control system shown in FIG. 2 will now begenerally described in reference to FIG. 3 wherein the abscissarepresents time in ms. and the ordinate represents signal levels. Beforetriggering, the illustrative firing command delays of 10 ms., 9 ms., 1 1ms., and 8 ms. are set on the respective digital switches 10-1, 10-2,10-3, and 10-4. These delays are intended to provide simultaneous firingof the guns 1, 2, 3, and 4 with actual firing delays of 20 ms. wherecharacteristic firing delays of 10 ms., 1 1 ms., 9 ms., and 12 ms. havebeen assumed. For purposes of explanation, these desired firing commanddelays, which are digitally represented in the system of FIG. 2, havebeen shown in analog form.

The system is now triggered by the system firing command FC, and countbegins to accumulate in the counters 20 and 22. As the count, whichrepresents elapsed time since system firing command FC coincides withthe firing command delay setting on the switch 10-4, the coincidencedetector 24 is satisfied and a firing command FC, is simultaneouslygenerated for gun 4 after 8 ms. As the count continues to accumulate,firing commands are similarly generated for guns 2, 1, and 3 after 9,10, and 11 ms. respectively. The guns are then fired simultaneously at20 ms. after different characteristic firing delays of the guns.

Throughout this sequence of events, counts have been accumulating ineach set of decade counters 26 and 28 representing elapsed times sincesystem'triggering, one count for each of the guns 1, 2, 3 and 4. As theguns are fired, the respective counts are terminated so as to representthe actual firing delays of 20 ms. between the system firing command FC,and the time breaks TB T3 T8 and TB,. These binary encoded firingdelays, each 20 ms. long, are then displayed in decimal form on theindividual displays 16-1, 16-2, 16-3, and 16-4.

If any of the displayed actual firing delays deviate from 20 ms., thisindicates that the assumed characteristic firing delay for theparticular gun( s) in question is incorrect. The correspondingswitch(es) 10 must then be reset to account for the true characteristicfiring delay. After continuous use, the characteristic firing delays ofa gun will vary. By use of this control system, such a variance caneasily be accommodated by merely watching the display 16 and resettingthe appropriate switches 10 as the need arises.

The digital circuitry of the firing command delay means 12 and theactual firing delay means 14 will now be described in detail withreference to FIGS. 4a, 4b, and 5. Referring to FIGS. 4a and 4b, thesource 18 comprises a unijunction l KHz oscillator 124, an inverter 126,a NAND gate 128 and a NAND gate 130 having one input connected to theoutput of the inverter 126 and the other input connected to the outputof the NAND gate 128. The unit decade counter 20 comprising a register132 is coupled to the output of the NAND gate 130 through an inverter134 and the tens decade counter 22 comprising a register 136 is coupledto the output of the register 132. When the system firing command PC,,is applied to the series of inverters 138, the registers 132 and 136 arereset through the inverters 140 and 142 and the NAND gate 130 is enabledby the NAND gate 128 to begin the continuously accumulating countrepresenting elapsed time since system triggering. As the countaccumulates in the counters 20 and 22, signals representing binaryencoded elapsed time are produced at the counter output terminals shownand applied to corresponding input terminals of the coincidence detector24.

The portion of the coincidence detector associated with gun I is shownin FIG. 5. By detecting a coincidence between digital signals from thecounters 20 and 22 which are applied at input terminals C1, C2, C4, C8,C10, C20, C40 and C80 and digital signals from the switch 10-1 which areapplied at switch terminals S1, S2, S4, S8, S10, S20, S40 and S80, thena signal representing the first command signal FC, may be obtained fromthe output of the detector.

The detector comprises a pair of parallel connected NAND gates 200associated with each of the input terminals C and S with one of the NANDgates 200 having inverters 202 in the input. The outputs of each pair ofparallel NAND gates 200 is then applied to a NAND gate 204. Byconnecting all of the units NAND gates 200 and all of the tens NANDgates 200 together and applying the output signals to the NAND gate 208connected to a one-shot multivibrator 210, a pulse of 25 ms. durationmay be obtained for use as the signal representing the firing command FCIdentical circuitry may be associated with the switches 10-2, 10-3, and10-4 for generating signals representing firing commands FC FC and FC,,.

Referring again to FIGS. 4a and 4b, each of the units decade counters 26comprising registers 150 and each of the tens decade counters 28comprising registers 152 are connected to the source 18 of gated clockpulses through NAND gates 154, which are enabled by flipflops 30, andseries-connected inverters 158. When the system firing command FC isapplied to the series of inverters 138 and resets the flip-flops 30through an inverter 160, the NAND gate 154 is enabled to initiate theaccumulation of a count in the registers 150 and 152 which have beenreset by the system triggering pulse through inverters 162, 164, and166.

The count accumulates in the pairs of registers 150 and 152 associatedwith the guns. Upon firing, signals representing the time breaks T8,,T8,, T8 and TB, are applied to the flip-flops 30 through Zener diodes168 and inverters 170 and 172 to terminate the accumulating count.Signals representing the binary encoded accumulated counts correspondingto the firing delays between system firing command FC, and the TBs ofthe guns are inverted by inverters 173 and appear at output terminals174. The binary encoded delay signals are then applied to correspondingterminals of the individual displays 16-1, 16-2, 16-3, and 16-4. A veryeffective display may be obtained by using lightemitting diodes in theindividual displays 16-1, 2, 3 and 4.

in order to generate a signal from the earliest firing of the four gunsor time break TB the outputs of the inverters 170 and 172 are ORed bymeans of a NAND gate 32. The output of the NAND gate 32 is then appliedto the seismic system through an inverter 176 and a one-shotmultivibrator 178 to stretch the pulse and immunize the TB against gunchatter. The width of the pulse is then reduced by an RC combination 180and inverters 182 and 184.

The digital control system described may be used to fire gunssimultaneously as shown and described. In the alternative, different orstaggered firing delay times may be set on the digital switches 10-1, 2,3 and 4 in the following manner so as to achieve a certain directivitywhere gun no. 1 is located at a water depth of 20 feet, gun no. 2 islocated at a water depth of 30 feet, gun no. 3 is also located at awater depth of 30 feet, and gun no. 4 is located at a water depth offeet. If it is assumed that the inherent firingdelay of all of the gunsare identical and equal to 12 ms., the switch 10-1 associated with gunno. 1 may be set for a 3 ms. firing command delay time to achieve a 15ms. firing delay. Digital switches 10-2 and 10-3 may both be set for 5ms. delays corresponding to a 17 ms. firing delay time since it takes 2ms. for the sound to travel 10 feet between gun no. 1 and guns nos. 2and 3. Digital switch 10-4 may be set to 7 ms. corresponding to a 19 ms.firing delay time since it takes sound 4 ms. to travel 20 feet betweengun no. 1 and gun no. 4. By utilizing the system in this manner tocontrol the firing of guns at different water depths during marineexploration, the primary pulse produced by the guns tends to bereinforced while the bubble pulse tends to be canceled.

Although the invention has been described in terms of the apparatus andmethod of operating a particular system, it will be understood that theinvention com- 6 prehends various modifications and equivalents of thatsystem which fall within the scope of the appended claims.

What is claimed:

1. A control system for firing a plurality of seismic sound sources byrespective firing commands in response to system triggering, comprising:

a means for presetting a variable firing command delay with respect tosystem triggering for each of said sound sources;

a means for determining the time elapsed after system triggering;

a means for detecting a coincidence between the time elapsed aftersystem triggering and said preset firing command delay for each of saidsound sources;

a means for generating'a firing command signal for firing each of saidsound sources in response to 'the respective detected coincidences;

a source of gated clock pulses; and

a means for displaying a count representing the overall firing delaytime with respect to system triggering for each of said sound sourcescomprising:

a firing delay register means associated with each of said sound sourcescoupled to said source of gated clock pulses for accumulating a countrepresenting elapsed time after system triggera gate means responsive tothe firing of each of said sound sources for terminating the furtheraccumulation of the count in each of said firing delay register means;and

a means for displaying the accumulated count in each of said firingdelay register means.

2. The control system of claim 1 comprising gate means for detecting thefirst firing of said sound sources.

3. A method of operating a control system for firing a plurality ofseismic sources, comprising the steps of:

presetting variable firing command delays for said respective soundsources;

triggering a firing cycle for said sound sources;

determining the elapsed time after triggering the firing cycle;

generating firing commands for said respective sound sources when theelapsed time equals the firing command delays;

determining the system firing delays represented by the elapsed timebetween triggering of the firing cycle and firing of said respectivesound sources; and

displaying said system firing delays for said respective sound sources.

4. The method of claim 3 wherein at least one of the firing commanddelay means is reset to correct for changes in the characteristic firingdelay of at least one of the sound sources as determined by the displayof the system firing delays.

5. A method of operating a control system for simultaneously orsequentially firing a plurality of pneumatic sound sources in which thesequence of the actual firing times of the sound sources are notidentical with the sequence of the firing commands applied to therespective sound sources, said difference in sequences being due todifferences in the characteristic firing delays of the sound sources,comprising the steps of:

generating a system firing command;

presetting variable firing command delays for said sound sources;

generating source firing commands for firing each of the sound sources,said source firing commands being delayed in time from said systemfiring command by the amount of the respective preset firing commanddelays;

generating time break signals upon the actual firing of said soundsources;

determining the elapsed time between the system firing command and thetime break for each sound source, said elapsed time representing boththe preset firing command delay and the characteristic firing delay forsuch source; and

adjusting said firing command delays to compensate for changes in thecharacteristic firing delays of the respective sound sources such thatthe elapsed times between generation of said system firing command andthe actual firings of the respective sound sources are maintainedsimultaneous or in the desired sequence.

6. A system for marine seismic exploration, comprising:

a plurality of pneumatic sound sources having characteristic delay timesfrom the application of a source firing command to the actual firing ofthe source sound which vary with usage, comprising:

means for generating a system firing command;

a source of gated clock pulses triggered by said system firing command;

a first counter having an input coupled to the output of said source ofgated clock pulses for accumulating a count corresponding to the timeelapsed after generation of said system firing command;

means for presetting a variable firing command delay for each of saidsound sources;

a coincidence detector with a first input coupled to the count output ofsaid first counter and a second input coupled to the variable firingcommand delays for generating a source firing command for each of saidsound sources upon the coincidence between the count in said firstcounter and the preset firing command delay for the respective soundsource;

means for generating a time break upon the actual firing of said soundsources;

second counters for each of said sound sources having inputs coupled tothe output of said source of gated clock pulses for accumulating countsrepresenting the elapsed time after generation of the system firingcommand;

gate means responsive to said time break signals for terminating thefurther accumulation of counts in each of said second counters; and

means for displaying the accumulated count in each of said secondcounters whereby the variable firing command delays for each of thesound sources may be adjusted to compensate for variations in saidcharacteristic delay times so as to permit the desired sequence of soundsource firings to be maintained.

1. A control system for firing a plurality of seismic sound sources byrespective firing commands in response to system triggering, comprising:a means for presetting a variable firing command delay with respect tosystem triggering for each of said sound sources; a means fordetermining the time elapsed after system triggering; a means fordetecting a coincidence between the time elapsed after system triggeringand said preset firing command delay for each of said sound sources; ameans for generating a firing command signal for firing each of saidsound sources in response to the respective detected coincidences; asource of gated clock pulses; and a means for displaying a countrepresenting the overall firing delay time with respect to systemtriggering for each of said sound sources comprising: a firing delayregister means associated with each of said sound sources coupled tosaid source of gated clock pulses for accumulating a count representingelapsed time after system triggering; a gate means responsive to thefiring of each of said sound sources for terminating the furtheraccumulation of the count in each of said firing delay register means;and a means for displaying the accumulated count in each of said firingdelay register means.
 2. The control system of claim 1 comprising gatemeans for detecting the first firing of said sound sources.
 3. A methodof operating a control system for firing a plurality of seismic sources,comprising the steps of: presetting variable firing command delays forsaid respective sound sources; triggering a firing cycle for said soundsources; determining the elapsed time after triggering the firing cycle;generating firing commands for said respective sound sources when theelapsed time equals the firing command delays; determining the systemfiring delays represented by the elapsed time between triggering of thefiring cycle and firing of said respective sound sources; and displayingsaid system firing delays for said respective sound sources.
 4. Themethod of claim 3 wherein at least one of the firing command delay meansis reset to correct for changes in the characteristic firing delay of atleast one of the sound sources as determined by the display of thesystem firing delays.
 5. A method of operating a control system forsimultaneously or sequentially firing a plurality of pneumatic soundsources in which the sequence of the actual firing times of the soundsources are not identical with the sequence of the firing commandsapplied to the respective sound sources, said difference in sequencesbeing due to differences in the characteristic firing delays of thesound sources, comprising the steps of: generating a system firingcommand; presetting variable firing command delays for said soundsources; generating source firing commands for firing each of the soundsources, said source firing commands being delayed in time from saidsystem firing command by the amount of the respective preset firingcommand delays; generating time break signals upon the actual firing ofsaid sound sources; determining the elapsed time between the systemfiring command and the time break for each sound source, said elapsedtime representing both the preset firing command delay and thecharacteristic firing delay for such source; and adjusting said firingcommand delays to compensate for changes in the characteristic firingdelays of the respective sound sources such that the elapsed timesbetween generation of said system firing command and the actual firingsof the respective sound sources are maintained simultaneous or in thedesired sequence.
 6. A system for marine seismic exploration,comprising: a plurality of pneumatic sound sources having characteristicdelay times from the application of a source firing command to theactual firing of the source sound which vary with usage, comprising:means for generating a system firing command; a source of gated clockpulses triggered by said system firing command; a first counter havingan input coupled to the output of said source of gated clock pulses foraccumulating a count corresponding to the time elapsed after generationof said system firing command; means for presetting a variable firingcommand delay for each of said sound sources; a coincidence detectorwith a first input coupled to the count output of said first counter anda second input coupled to the variable firing command delays forgenerating a source firing command for each of said sound sources uponthe coincidence between the count in said first counter and the presetfiring command delay for the respective sound source; means forgenerating a time break upon the actual firing of said sound sources;second counters for each of said sound sources having inputs coupled tothe output of said source of gated clock pulses for accumulating countsrepresenting the elapsed time after generation of the system firingcommand; gate means responsive to said time break signals forterminating the further accumulation of counts in each of said secondcounters; and means for displaying the accumulated count in each of saidsecond counters whereby the variable firing command delays for each ofthe sound sources may be adjusted to compensate for variations in saidcharacteristic delay times so as to permit the desired sequence of soundsource firings to be maintained.